The vehicle wheel bearing apparatus rotatably supports a wheel hub for mounting a wheel, via a rolling bearing, for a driving wheel and for a driven wheel. For structural reasons, an inner ring rotation type is used for the driving wheels and both inner ring rotation type and the outer ring rotation type are used for the driven wheels. In general, the wheel bearing apparatus is classified as a so-called first, second, third or fourth generation type. In a first generation wheel bearing, it includes double row angular ball bearings fit between a knuckle and a wheel hub. In a second generation type, a body mounting flange or a wheel mounting flange is directly formed on the outer circumference of an outer member. In a third generation type, one of inner raceway surfaces is directly formed on the outer circumference of a wheel hub. In a fourth generation type, the inner raceway surfaces are directly formed on the outer circumferences, respectively, of a wheel hub and an outer joint member of a constant velocity universal joint.
The wheel bearing apparatus is usually arranged in a position on the vehicle where it is likely to be splashed with muddy water etc. Thus, it has sealing means to seal a space between an outer member and an inner member of the wheel bearing apparatus. As a result of verifying the damaged conditions of wheel bearing apparatus recovered from the market, it has been found that the wheel bearing apparatus has been damaged at a high proportion due to troubles caused by the sealing apparatus rather than natural causes, such as wear or peeling. Accordingly, the expected life of the bearing apparatus could be increased by improving the sealability and durability of the sealing means.
Several sealing structures have been proposed to improve their sealability. One representative example of a wheel bearing apparatus of the prior art equipped with such a sealing structure is shown in FIG. 10. This wheel bearing apparatus has an outer member 50 secured on a vehicle body via a knuckle. The outer member includes double row outer raceway surfaces 50a, (50a) formed on its inner circumference. In addition, a wheel hub 53 and an outer joint member of a constant velocity universal joint (not shown) are rotatably mounted on the outer member 50, via double row balls 52, (52), held equidistantly along their inner and outer raceway surfaces.
An inner raceway surface 53a is formed on an outer circumference of the wheel hub 53. The inner raceway surface 53a corresponds to one of the double row outer raceway surfaces 50a, (50a). A wheel mounting flange 54 is also formed on one end of the wheel hub 53. A brake disk and a wheel (not shown) are mounted on the outer wheel mounting flange 54.
A sealing structure 55 comprises an inner-side surface 54a of the wheel mounting flange 54, a metal core 56 fit into the inner circumference of the outer member 50, and an elastic sealing member 57 secured on the metal core 56. The elastic sealing member 57 includes two axial lip portions 58. The two lip portions 58 axially contact the side surface 54a of the wheel mounting flange 54. A radial lip portion 59 radially contacts the outer circumference of the wheel hub 53.
In addition, the metal core 56 has a radially extending weir portion 56a. The weir portion 56a is adapted to be in close contact with the outer-side end face of the outer member 50. This weir portion 56a is formed with a circular arc-shaped (i.e. crescent-shaped) configuration. Also, it is arranged in an upper-half region of the wheel bearing apparatus.
The sealing structure 55 prevents muddy water from flowing toward the side surface 54a of the wheel mounting flange 54, due to the presence of the weir portion 56a, when muddy water splashes over the outer member 50 during running of a vehicle. Accordingly, it is possible to prevent muddy water from remaining around the axial lip portions 58. Thus, it is possible maintain the sealability of the wheel bearing apparatus. See, Japanese Laid-open Patent Publication No. 2003-49852.
However, in such a sealing structure 55, it is necessary to set a small gap between the metal core 56 and the side surface 54a of the wheel mounting flange 54 in order to keep a desirable contact pressure of the axial lip portions 58 against the side surface 54a. This brings limitations in the degree of freedom in design of the wheel bearing apparatus. In addition, the weir portion 56a, having a crescent shape, is arranged only in an upper-half region of the wheel bearing apparatus. Thus, it is necessary for the weir portion 56a, at an upper-half region of the wheel bearing apparatus, to have the metal core 56 press-fit onto the outer member 50 during assembly of the wheel bearing apparatus. This increases assembling steps and time and thus the manufacturing cost. Furthermore, it is believed that the weir portion 56a would be plastically deformed by an impingement of pebbles, etc. during running of the vehicle.